User review: YINDING YD-2XU2 (Gemini Duo clone)

Nobody has written a review of this popular light so I'll do it
Sorry for any possible errors or weird spelling - english is not my native language. Feel free to ask me any questions about this light, I'll try to answer them all.

PACKAGING / CONTENTSCardboard "gift box", used for many chinese bike lights:
You'll get the light, battery, charger, headstrap mount, 2 rubber rings for handlebar mount and the box.
DESIGN
This light is a direct copy of Gemini Duo and probably the smallest 2 XML light that you can buy atm.Gemini Duo ? 2013 Mtbr Lights Shootout | Mountain Bike ReviewGemini Duo 4 Cell front light - BikeRadarGemini Duo: Nine Brilliant, High-Powered Lights | Bicycling Magazine
You can read reviews of the original at the links above, most of the info there can be applied to this clone. Main differences between the original and the clone are much worse battery and 3 fixed brightness levels on clone vs 3 programmable levels on original.
Light's head is very small with 2 plastic TIR lenses over the leds. Weight of the head is only 59g, dimensions are 44x23x34mm without plastic mount.
There is a single button on the back with model name engraved near it.

Yinding compared to SolarStorm X2 and Fandyfire D99 (another simular light with TIR lenses, but a bit larger and heavier).

It has a magicshine-style connector, mount with piece of rubber glued on it (thats a sign of good quality light, cheaper lights don't use rubber there) and waterproof o-ring on the power cable.
You can also rotate the mount, another rare feature for chinese lights.
Mounting area is flat without any cable holes so you can use/make your own mount, see post #11 for example:User review: YINDING YD-2XU2 (Gemini Duo clone)
BATTERY
Usual cheap chinese battery, 4x18650 2S2P cells in shrinkwrap, 7.4v voltage. Not waterproof! You have to cover it in plastic bags/rubber balloon/gloves or something to protect it from water or it'll short-circuit like this:
Battery capacity is kinda ok for chinese batteries but still horrible. I have 2 lights and here are the discharge graphs for them:
Battery 1, 3600mAh with very weird unstable voltage on discharge cycle.
Battery 2, 3200mAh with good stable voltage.
Both of these batteries will work for about 2 hours on high mode and imo you should replace them with something better from Xeccon/Magicshine/Gemini.

UI
4 modes, switched with single click in this sequence: off-low-mid-high-off and repeat. Strobe on hold, high frequency, not very usable imo.
TEARDOWN
Lets open it up and see how its made
Starting from the mount:
3mm hex screw, plastic mount, 2 rubber o-rings between the screw, mount and the case.
O-rings removed. These o-rings will hold the mount at any angle so you can turn it and leave at specific angle that you need.
Nothing else on the bottom so lets move to the front.
2 small hex screws (about 1.5mm) hold the front part of the case. Removing the screws and front part gives us access to the 2 plastic TIR lenses and XM-L2 leds. Both lenses and the front part of the case have rubber o-rings under them so this light should be competely waterproof.
Leds are mounted on aluminium backplate and connected in series. You can also see that this specific version has XM-L2 leds (silver color of the led, 2 bounding wires instead of 3 on 1st gen) which the seller replaced himself...and it wasn't a very good job - there are fingerprints all over the plate and wires soldering is not very good.
Moving on, next we have to remove 2 screws on the sides of led's backplate:
These long screws are connected to the back side of the case.
With screws removed we can also lift up led's backplate to discover proper amount of good thermal paste underneath - everything is ok here. And here is an important part - led's backplate is mounted directly on the outer case, there is no additional pills here so thermal transfer is excellent (unlike D99 where leds were basically handing in air).
Moving on to the back, another view of the case inside and metal wall in the middle. There is a small hole in the center for led's wires and a hole on the side for power wire. Power wire doesn't have any pull-out protection so be careful with it.
2 pics of the driver and we're done. Soldering looks good everywhere, driver is marked "HX-1343". There are 2 smd leds for battery charge level indication, R110 current sense resistor that you can replace to increase current on leds (not recommended though, case can't really handle any additional heat).
ELECTRONICS
This time I'll use a picture with every measurement:

A few addional notes about it:
Current from battery is measured on external PSU set at 7.5v, thats the average voltage on discharge cycle. You can divide your battery capacity on current to get estimated runtime in hours (for the included battery at high mode its 3200/1700 = 1.88 hours, a good quality battery like Xeccon 5200mAh will give you 3.06 hours).
There are 2 values for current on leds because driver is a bit weird...it usually outputs 1.7A on high, BUT when input voltage is 6.9-7.2v it jumps to 2A. I have no idea why this is happening, but I double checked everything and it just works like this.
Driver will go out of regulation at 6.4v on input = leds will start to dim. This is a good feature as you'll notice that even if your light is mounted on helmet and you can't see the battery indicator on it. At about 5v it will turn off competely.
Lumens output is a very rough estimation (I don't have integrated sphere to properly measure lumens output) based on this calculator:LEDCalc.fonarevka.ru
And with 20% reduction for losses in optics to calculate estimated OTF lumens. Still it should be close to real output, I verified that by calculating and comparing results for other lights/flashlights.IMPORTANT NOTICE!This light is very small and very lightweight so it will heat up VERY FAST. While moving it will be cooled by air so its not a problem, but don't run it on high mode for a long time when standing still - it can and will overheat very easily.
Some users have reported that it has overheat protection that will dim/turn off the light but I haven't tested that and I don't recommend to rely on such protections - overheating is bad for leds and electronics.

Originally Posted by znomit

Tested the thermal cutoff today.
Cuts in around 70C (IR thermometer).
No hysteresis so theres a bit of flicker before it come fully on… guess thats a good visual warning. Cuts all modes back by half.

BEAM PROFILE
Compared to D99 on the right:
D99 uses the same type of lenses with wider angle (probably 22-30 degrees compared to 15 on Yinding) so the beam is almost the same. Its wider on D99 but its hard to notice on that picture.
Compared to SolarStorm X2 on the right:
Here you can see the difference between TIR lens and reflector. Reflectors on SSX2 have noticable sidespill and tight hotspot in the center while TIR on Yinding gives just one wide hotspot.
You can also see the difference in color temperature in both pictures. Neutral-white XM-L2 leds have more natural-looking slightly yellow color vs blue-white color of typical cheap chinese cool white XM-L leds.
BEAMSHOTS
2 simple beamshots on the ceiling:
This light uses TIR lenses (probably 15 degree wide like these ones 15 Degree Angle LED Optical Lens - Black - Free Shipping - DealExtreme) that give it a wide and floody hotspot with gradual fade at the edges, which is less tiring on the trail than usual high contrast reflector lights. Not a very good thrower though but should be an excellent light for the bars.
Its not a pure flood light and not a thrower, its somewhere in between and works great as a single light for low and medium speed riding on the roads/trails.
And a beamshot on the road, sorry for cellphone quality:
And here are some beamshots stolen from another threads and sites

CONCLUSION

Pros:
Very small, very light.
Good mount.
Good wide-hotspot beam.
Excellent thermal transfer from leds to outer case.
XM-L2 neutral white leds in this version, better color rendition and easier on eyes compared to cool white.

Cons:
Bad batteries.
Overheats very easily.
No brightness levels adjustment like on original Gemini Duo.

Overall - great light imo, one of the best chinese lights atm. Not very powerful but so small and light! I will probably use it myself as a backup light for long rides, it doesn't take much space on the handlebars and provides good amount of light for forest/trails riding.

And another review done! Will proofread it tomorrow and fix any errors.
It's getting cold and rainy here so hopefully I'll have more time to write my reviews. Next up is Xeccon Spiker 1206 review/comparison with cheap chinese 1xml light, I'll try to show what you're paying for when buying expensive brand name lights. After that - huge Solarstorm X2 comparison, got 9 samples here to show all the variety and lottery of popular chinese bike lights (spoiler alert - expect _horrible_ batteries and random output/random quality ).

Pros:
Very small, very light.
Good mount.
Good floody beam.
Excellent thermal transfer from leds to outer case.
XM-L2 neutral white leds in this version, better color rendition and easier on eyes compared to cool white.

Cons:
Bad batteries.
Overheats very easily.
No brightness levels adjustment like on original Gemini Duo.

Great review...let me add a few cents

Pros:
Even XML U2 version has quite nice white color light
The cable does not come out at the mount area and this area is flat. That means you can easily adjust your own mount...like this (This goes for 880clone and SSX2 as well)

Cons:
there is small weak point for water...that are the screws for front panel. I wraped screws with teflon tape and now I can throw it in water and be very confident. (excluding the battery)
no memory mode...at least press and hold function should be off and not strobe.
Mounting O-rings are really crapy!!! Buy silicone ones!

*the beam is actually quite tight, no where near to flood. That would be MJ872. You could say it is very floody spot light. I think perfect beam for helmet light for off road use.
*battery is not that bad compare to other cheap bike light sets. (3x clone, SSX2...) I measured my pack to around 3500+mAh. (MJ828 battery has just 10-20% more capacity and it costs almost as Yinding whole set.)

Seems all the places are out of the ~$50 and now its ~$80....that is Gemini territory (light head only...which is all you are really getting here).

Not really, head only is $43 shipped on aliexpress while gemini duo is $93+shipping on action led lights.

bhocewar, I dont think that water can get through screws in front unless you're submerging it in water
Floody spot light is a good description for it. I'll make a few rides and then update info about beam profile. 15 Degree Angle LED Optical Lens - Black - Free Shipping - DealExtreme - looks very simular so its TIR lenses could be 15-20 degrees too, which is kinda tight but with good hotspot brightness.

MK96, of course its done by hand - oven is too expensive And I actually can make a much better soldering myself.

The fact that the AMPS get higher as the battery depletes is good news, it has either a buck or boost driver. A lot of cheap chinese lights use linear drivers which means the light output decreases as the batteries deplete. Case in point given an hours usage a light that starts out at say 1400l will probably drop well below 1000l.

Buck/boost drivers increase the current as the battery voltage decreases, meaning light output remains the same until the batteries are almost fully depleted. I bet this light pumps out more lumens after 15-20 minutes than most cheap chinese lights that are said to pump out 1200+ lumens, and the superior heat design will also contribute to better and longer lasting brightness.

I know that the one from Aliexpress is no longer available, but you mention "custom version with XM-L2 neutral white leds". Is this a noticeable difference? I know that the ~$50 offering from fasttech has a less than optimal battery -- but I will be replacing that with something from Xeccon (hopefully small one for helmet and larger one for bars). Will be using for commuting and when timing works out - nite riding/24 hr racing. Thoughts on the charger from the fasttech offering (safety), and how are people doing custom/semi-custom helmet mounts.